Method of removing beer stone milk stone and railway carriage encrustations using a diphosphonic acid

ABSTRACT

WHEREIN R IS AN ALKYL GROUP HAVING FROM 1 TO 11 CARBON ATOMS, X&#39;&#39; IS OH OR NH2, AND ALKALI METAL, AMMONIUM AND ACID SALTS OF SAID DISPHOSPHONIC ACID, TO REMOVE SAID ENCRUSTATIONS.   R-C(-P(=O)(-OH)2)2-X&#39;&#39;   A METHOD FOR THE REMOVAL OF GROSS TENACIOUS ENCRUSTATIONS SELECTED FROM THE GROUP OF ENCRUSTATIONS CONSISTING OF BEER STONE, MILK STONE, AND ENCRUSTATIONS ON THE EXTERIOR SURFACE OF RAILWAY CARRIAGES, COMPRISING APPLYING THERETO AN EFFECTIVE AMOUNT OF AN AQUEOUS SOLUTION CONTAINING AT LEAST ONE DIPHOSPHONIC ACID OF THE FORMULA

United States Patent 3,634,25j METHOD (NF REMOVlNG BEER TONE, MILK STONE AND RAILWAY CARGE ENCRUSTA- 'IIONS UING A DHPHOSPHONEC ACID Alan S. Porter, Halesowen, Birmingham, and David Thomas Kerr Whytc, Dudley, England, assignors to Electric Reduction Company of Canada Ltd, lslington, Ontario, Canada No Drawing. Filed Apr. 24, 1968, Ser. No. 723,946 Claims priority, application England, Apr. 26, 1967, 19,193/67 int. Cl. (102i) /06; (323g 1/06 US. Cl. 252-37 14 Claims ABSTRAQT OF THE DISCLOSURE A method for the removal of gross tenacious encrustations selected from the group of encrustations consisting of beer stone, milk stone, and encrustations on the exterior surface of railway carriages, comprising applying thereto an effective amount of an aqueous solution containing at least one diphosphonic acid of the formula wherein R is an alkyl group having from 1 to 11 carbon atoms, X is OH or NH and the alkali metal, ammonium and acid salts of said diphosphonic acid, to remove said encrustations.

The present invention relates to the removal of tenacious encrustations from rigid surfaces.

During fabrication or use many rigid surfaces become coated with tenacious encrustations which cannot successfully be removed by washing of the surface. In certain cases it is possible to remove the encrustations by physical means, for example by beating with a hammer or by the use of a wire brush. However, such methods are not suitable for use in confined spaces, for example the interior of boilers or other apparatus, or upon large areas. It has therefore been customary to use other methods to remove the encrustations, for example by washing the surface with solutions of various descaling compositions, including acids such as sulphamic or oxalic acid. However, even though such treatments may remove certain types of encrustation they are not successful in all respects. For example sulphamic acid removes a major proportion of the brake-block particles which stick to the surfaces of railway rolling stock, but leaves an insoluble residue which progressively accumulates.

We have now found that certain phosphonic acids and their salts may be used to remove a wide variety of encrustations containing calcium carbonate and/or iron compounds from rigid surfaces.

Whilst the phosphonic acids for present use are known to possess sequestering properties we do not believe that the removal of encrustations by the acids involves this property, since conventional sequestering agents are not normally effective in removing encrustrations. Moreover the phosphonic acids for present use are not as strong as some acids which have hitherto been used. It is therefore surprising that the phosphonic acids should be successful for the removal of iron-containing encrustations which other commonly used cleaners are often unable to remove satisfactorily.

The present invention provides a method for the removal of calcium carbonate and/or iron containing encrustations from rigid surfaces which comprises applying thereto an aqueous solution comprising an acid having the general formula:

(wherein R is an alkyl group containing up to 11 carbon atoms and X is an OH or NH; group) or an alkali metal or ammonium salt or acid salt thereof. The preferred acids for present use are those wherein R is a lower alkyl group such as a methyl, ethyl or propyl group, especially a methyl group, and X is an OH group.

The phosphonic acids for present use may be conveniently prepared by the reaction of phosphorus trichloride or phosphorus acid with an acylating agent and steam distilling the reaction products. An especially preferred method for the preparation of the phosphonic acids is that described in US. Pat. No. 3,468,935, wherein phosphorus trichloride is reacted with an excess of glacial acetic acid and the reaction roducts are steam distilled.

The phosphonic acids or phosphonate salts may also be used in conjunction with other scale removing acids conventionally used in the removal of encrustations, for example, with citric, oxalic or sulphamic acids. The amount of other acid present in the mixture is preferably from 25 to by weight thereof. The phosphonic acids or their salts may also be used in admixture with other conventional ingredients such as surfactants.

The phosphonic acids and phosphonate salts may be used in the conventional manner, that is by dissolving acid, together with any other ingredients, in water. It is usual to prepare a solution containing a total acid concentration of at least 10 preferably 20 to 250 grams per litre. This aqueous solution may then be applied to the rigid surface at temperatures varying from ambient to C., either as a wash or by immersing the encrusted articles in the solution. The amount of the solution used will depend upon the nature of the encrustation to be removed. For example, we have found, that when the method of the invention is used to remove scale or rust, the use of approximately twice the stoichiometric amount of phosphonic acid required, based upon the iron content of the encrustation, produces satisfactory results.

The method of the invention finds use in the treatment of a wide variety of rigid surfaces to remove different encrustations therefrom. For example, it finds use in the removal of calcareous deposits such as milk-stone and beer-stone from dairy and brewery equipment; and in the removal of water scale from stills and evaporators. The method of the invention is of especial application in the removal of iron containing encrustations such as mill scale from the tubes of tubular boilers prior to their commissioning. In such use the desired amount of crystalline acid is added to water circulating through the boiler, which water may be added at ambient or raised temperatures, for example up to about 100 C. The method of the invention also finds use in the cleaning of the exterior of railway rolling stock to remove brake-block particles. In this latter use, the phosphonic acids or their salts may be applied as a concentrated aqueous solution or paste to the surface and then removed by washing down with water. We have found that in general the method of the invention is more effective in removing iron encrustations when there is present a proportion of metallic or ferrous iron in the encrustations.

Where the method of the invention is used to remove iron-containing encrustations we have found that ammonia is of benefit. The ammonia may be used as an after treatment following the treatment with the acid or, more preferably, in admixture with the acid. The amount of ammonia employed is preferably at least 2, especially 2 to 4, molar proportions per molar proportion of acid of the invention. The use of ammonia inhibits the formation of sludges during the action of the acid on the encrustation. Surprisingly we have also found that the use of ammonia inhibits corrosion of the cleaned surfaces.

The invention will now be illustrated by the following examples in which all weights refer to anhydrous materials except where the contrary is specified.

EXAMPLE 1 A solution (25 ml.) containing l-hydroxyethylidene- 1,1-diphosphonic acid (206 g./l.) at 80 C. was poured on to calcium carbonate beads (1 g.). The beads dissolved completely with brisk evolution of CO EXAMPLE 2 Solutions of the acids (100 ml. containing 20 g./l.) listed were boiled with samples of iron powder (1 g.) for 30 minutes and the amount of iron dissolved was then determined.

Acid: Weight of iron dissolved g.) 1-hydroxyethylidene-1,1-diphosphonic 0.25

1 hydroxyethylidene 1,1-diphosphonic +3.4

g./l. ammonia 0.60 Oxalic acid dihydrate 0.04 Citric acid monohydrate 0.73

EXAMPLE 3 Solutions (100 ml.) of the acids listed were boiled for 30 minutes with samples of dust (1 g.) from the outside of railway carriages. This dust consists mainly of iron oxides with, possibly some elemental iron. The weight of dust dissolved, calculated as Fe O is shown below.

Weight dissolved (g. as FczOa) Cone. Acid (ll-I l hydroxycthylidene-l,1-dipl1osol1onic l-hydroxycthylidene-l,l-diphosphonic Oxalic acid dihydrate l-hydroxyethylidcne-l,1-diphosphonic Sulpliamic acid Oxalie acid dihydrate" Sulphamie acid Citric acie monoliydrate IONMHHHHN oooooooo l-hydroxyethylidene-1,1-diphosphonic acid alone, or in a 1:1 weight mixture with oxalic acid, is more effective than oxalic acid alone (which is commonly used for cleaning carriages). The 1:1 weight mixture of l-hydroxyethylidene-l,l-diphosphonie acid with sulphamie acid is better than either acid alone.

EXAMPLE 4 Effect of acid treatment Mill scale removal but white deposit formed, becoming green on drying.

Mill scale removal Rusted slowly.

Effect of exposure Acid to atmosphere l-hydroxyethylid enc- 1,1-diphosphonic.

No change.

l-hydroxyetliylidenc- 1,1-diphosphonic plus 3.4 g./l. ammonia.

l-hydroxyethylidcnel,1-diphosphonic plus 5.1 g./l. ammonia.

l-hydroxyethylidene- 1,1-diphosphonic plus .....de Did not rust.

..d Do.

(3.8 g./l. ammonia. Citric acid monohydrate do Rusted slowly.

plus 3.4 g./l. ammonia.

Rusted.

Sulphamic acid Mill scale only partly removed. Hydrochloric acid Mill scale removed Rusted very rapidly.

We claim:

1. A method for the removal of gross tenacious encrustations selected from the group of encrustations consisting of beer stone, milk stone, and encrustations on the exterior surface of railway carriages, comprising applying thereto an eifective amount of an aqueous solution containing at least one diphosphonic acid of the formula wherein R is an alkyl group having from 1 to 11 carbon atoms, X is OH or NH and the alkali metal, ammonium and acid salts of said diphosphonic acid, to remove said encrustations.

2. A method according to claim 1 wherein R is a lower alkyl group.

3. A method according to claim 2 wherein said solution contains CH COH(PO H 4. A method according to claim 3 wherein the solution contains at least one other scale removing acid.

5. A method according to claim 3 wherein the solution contains a surfactant.

6. A method according to claim 3 wherein the solution is employed in conjunction with ammonia.

7. A method according to claim 3 wherein said aqueous solution has a total acid concentration of between 10 and 250 grams per liter.

8. A method according to claim 7 wherein said acid concentration is between 20 and 250 grams per liter.

9. A method according to claim 8 wherein said aqueous solution contains 2 to 4 molar proportions of ammonia per molar proportion of said diphosphonic acid.

10. A method according to claim 9 wherein said aqueous solution also contains at least one acid selected from the group consisting of citric acid, oxalic acid and sulphamic acid.

11. A method according to claim 2 wherein said aqueous solution has a total acid concentration of between 10 and 250 grams per liter.

12. A method according to claim 11 wherein said acid concentration is between 20 and 250 grams per liter.

13. A method according to claim 12 wherein said aqueous solution contains 2 to 4 molar proportions of ammonia per molar proportion of said diphosphonic acid.

14. A method according to claim 11 wherein said aqueous solution also contains at least one acid selected from the group consisting of citric acid, oxalic acid and sulphamic acid.

References Cited UNITED STATES PATENTS 3,317,340 5/1967 Ziehr 1343 X 3,431,217 3/1969 Hwa 252389 3,477,956 11/1969 Stanford 25282 3,481,869 12/1969 Jones 25287 X JOHN T. GOOLKASIAN, Primary Examiner M. E. MCCAMISH, Assistant Examiner US. Cl. X.R. 

